Textured catalysts, methods of making textured catalysts, and methods of catalyzing reactions conducted in hydrothermal conditions

ABSTRACT

A textured catalyst having a hydrothermally-stable support, a metal oxide and a catalyst component is described. Methods of conducting aqueous phase reactions that are catalyzed by a textured catalyst are also described. The invention also provides methods of making textured catalysts and methods of making chemical products using a textured catalyst.

STATEMENT OF GOVERNMENT RIGHTS

This invention was made with Government support under contractDE-AC0676RLO 1830 awarded by the U.S. Department of Energy. TheGovernment has certain rights in this invention.

FIELD OF THE INVENTION

The present invention relates to textured catalysts and methods ofmaking textured catalysts. The invention also relates to the use oftextured catalysts as catalysts for reactions conducted in hydrothermalconditions.

BACKGROUND OF THE INVENTION

For many years there has been active and increasing interest inconducting chemical processing in aqueous media. In many cases, apotential feedstock is produced along with water. This occurs, forexample, in the commercial maleic anhydride process. Alternatively, inthe case of fermentations, potential feedstocks are themselves producedin water. Removal of water from these compositions would betime-consuming and costly. Additionally, water has many advantages overmore conventional solvents that present problems with toxicity anddifficulties with handling and disposal.

On the other hand, water is a relatively reactive medium and mostconventional catalysts would quickly become deactivated. To overcomethis problem, several workers have conducted aqueous phase reactionsover carbon-supported catalysts. For example, Olsen in U.S. Pat. No.4,812,464 described certain aqueous phase hydrogenations over apalladium on carbon catalyst. Schwartz in U.S. Pat. No. 5,478,952described the use of catalysts composed of highly dispersed rutheniumand rhenium on a carbon support for catalyzing aqueous phasehydrogenations.

Unlike many oxide supports, carbon supports can maintain their integrityunder aqueous, acidic or basic reaction conditions. Carbon supports arealso available with exceptionally high surface areas allowingpreparation of catalysts with a high dispersion of active metals.Unfortunately, much of the surface area is contained within smallmicropores, which can result in severe mass transport limitations. As aconsequence, many carbon supports are prepared as very fine powders tominimize mass transport effects due to pore diffusion limitations.

It has been found that many catalytic metals, once reduced, are nottightly bound to a carbon surface. During operation, these loosely boundcatalytic metals can sinter, or agglomerate, thereby greatly reducingthe available catalytic surface area. To lessen the effects ofsintering, manufacturers typically limit the amount ofcatalytically-active metal to less than 1 weight percent of the totalcatalyst. While this results in a more efficient use of catalytic metal,it requires a larger bed to achieve the required conversions.

To improve properties of carbon-based catalysts, Heineke et al., inCanadian Patent No. 2,191,360, described certain carbon-based catalystshaving a titania coating. In the invention of Heineke et al., a carbonsupport is treated with a Ti or Zr alkoxide, halide or mixedalkoxide-halide. Suitable carbon supports are generally suspendedgraphite or activated charcoal. Treatment of the carbon support with theTi or Zr compound is preferably carried out in anhydrous solvents. Thereaction is terminated by quenching with a small amount of water. Thecatalysts are then prepared by precipitating platinum in an aqueousmedium using a reducing agent. In the examples, Heineke et al. suspendedgraphite particles in dry n-butanol and added titanium tetraisopropoxideor titanium tetrachloride followed by stirring for 2 days. Then waterwas added and the resulting particles are filtered off and dried. Theresulting material was treated with an aqueous solution ofhexachloroplatinic acid at a pH of 2.75. The platinum was precipitatedby addition of sodium formate. The catalysts were tested in thehydrogenation of NO to NH₂OH. Compared with catalysts lacking thetitania layer, Heineke's catalysts showed better NH₂OH selectivity(86.77 and 91.96 vs. 86.36 and 89.90) and space-time yield (0.798 and0.897 vs. 0.788 and 0.870).

Despite these, and many other efforts, there remains a need forcatalysts having new properties, especially catalysts that are stable inaqueous phase conditions. There also remains a need for new andcost-effective methods of making catalysts. There further remains a needfor new aqueous phase catalytic reactions.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a textured catalyst comprisinga hydrothermally-stable, porous support comprising a porous interior andan exterior surface; a metal oxide; and a catalyst component. The poroussupport has a minimum, smallest dimension of at least about 100 μm.Viewed in cross-section, at least about 70% of the catalyst component iswithin about 5 μm of the minimum cross-sectional area that encompassesabout 80% of the metal oxide. Also, at least about 5% of the catalystcomponent is at least about 10 μm from the exterior of the support.

In a second aspect, the invention provides a method of making acatalyst. This method includes: providing a porous,hydrothermally-stable support; forming a sol comprising metal oxideparticles; adding a catalyst component; and drying. The porous,hydrothermally-stable support is directly contacted with a solcomprising metal oxide particles.

The invention also provides a method of conducting a catalyzed reactionunder hydrothermal conditions. In this method, at least one reactantpasses into a reaction chamber. The reactant is in an aqueous solution.A catalyst is present in the reaction chamber. This catalyst was made byforming a sol of a metal oxide at a pH that is within 2 of the pH of theaqueous solution; adding a catalyst metal; and depositing the metaloxide and the catalyst metal onto a porous, hydrothermally-stablesupport. The at least one reactant is reacted in the presence of thecatalyst and under hydrothermal conditions. At least one product isobtained from the reaction chamber. The product obtained has a higherpurity or a higher yield than the product obtained in a comparative testunder similar conditions except where the reaction is conducted at a pHthat is 4 or greater than the pH of the aqueous solution.

The invention further provides a method of conducting a catalyzedreaction under hydrothermal conditions, comprising: passing at least onereactant into a reaction chamber; reacting the at least one reactant inthe presence of the catalyst and under hydrothermal conditions; andobtaining at least one product from the reaction chamber. In thismethod, the reactant is in an aqueous solution. A catalyst is present inthe reaction chamber. The catalyst includes: a porous,hydrothermally-stable support; a metal oxide disposed on the support;and a catalyst component.

Catalysts of the invention (which may be termed “textured” catalystsbecause the metal oxide imparts additional “texture” to the poroussubstrate) can be active and stable, even in aqueous conditions. Thetextured catalysts can also offer other advantages, such as selectivity.Compared to conventional catalysts and reactions using conventionalcatalysts, the inventive catalysts and reactions can exhibitunexpectedly superior properties. For example, the inventive catalystshaving a metal oxide coating on activated carbon can provide (a) betterdispersion of the active metal on the catalyst surface, (b) betterstability of the active metal on the catalyst (as opposed to putting theactive metal directly on the carbon), and (c) enhanced activity andselectivity. The texturing agent may also be responsible fordistributing active components primarily in larger pores such thatreactions of substrate are substantially excluded from micropores,reducing diffusion limitations. If a substrate were to react in deeperpores, products that are easily susceptible to over-reactions may beless able to quickly diffuse out of the catalyst and be subject tocontinued interaction with active metal sites producing unwantedbyproducts. The texturing agent may also have the effect of ensuringthat the higher value catalytic metals are preferentially partitioned tothe easily accessible surface area over the deeper, less accessiblepores, thereby requiring less metal to achieve equivalent catalyticactivity over standard catalysts.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawings executedincolor. Copies of this patent or patent application publication withcolor drawings(s) will be provided by the Office upon request andpayment of the necessary fee.

FIG. 1 is a series of black and white photomicrographs of across-section of a textured catalyst obtained by scanning electronmicroscopy (SEM) at a series of magnification levels.

FIG. 2 is a series of SEM photomicrograph views obtained by elementmapping that show the distribution of Si (yellow), Zr (green) and Pd(red) in a cross-section of a freshly-prepared textured catalyst. Thesection of catalyst analyzed is the same as in the top-right of FIG. 1.

FIG. 3 is a series of SEM photomicrograph views obtained by elementmapping that show the distribution of Si (yellow), Zr (green) and Pd(red) in a cross-section of a freshly-prepared textured catalyst. Thesection of catalyst analyzed is the same as in the middle-left of FIG.1.

FIG. 4 is a black and white photomicrograph (×10000 magnification; 2.3cm=20 μm) of a cross-section of a textured catalyst after use andrecovery from a reaction apparatus. The numerical numbers indicate thespots where energy dispersive X-ray emission analysis (EDX) wereperformed.

FIGS. 5a-5 c show plots with intensities due to emissions of C, Pd andZr nuclei at the locations identified in FIG. 4 as 1 (FIG. 5a), 2 (FIG.5b) and 3 (FIG. 5c).

FIG. 6 is a graph comparing the % conversion of succinic acid that washydrogenated in an aqueous solution under identical conditions exceptusing a 2.5 wt. % Pd/5.0 wt. % ZrO₂/carbon catalyst (upper curve) or a2.5 wt. % Pd/carbon catalyst (lower curve).

GLOSSARY OF TERMS

A “porous” material is one that has at least 10% porosity by volume.Porosity and pore size are typically measured by mercury porisimetry andnitrogen adsorption (BET).

“Hydrothermal conditions” are the presence of a water phase (more than asmall amount of dissolved water) at greater than 100° C. and pressuresof greater than 1 atm and may include supercritical conditions. A“hydrothermally-stable” material loses less than 15% of its surface areaafter 24 hours in water at 150° C. at the vapor pressure of water underthese conditions (with an initial loading of the material in water of 10g material/100 g water); more preferably, a “hydrothermally-stable”material loses less than 5% of its surface area after 72 hours in waterat 250° C. at the vapor pressure of water under these conditions.

A metal oxide “sol” is a suspension of oligomers and/or colloidalparticles, where monomers make up less than 50% of the metal mass of thecomposition.

The “smallest dimension” of a particle refers to the average minimumdimension, i.e. the average particle diameter in any direction. For twodimensions, this can be measured from a cross-section viewed by SEM. Forexample, in the wedge-shaped cross-section of the particle in FIG. 1,particle diameter would be measured at several points from the base tothe apex and averaged. Alternatively, the “smallest dimension” can bepartly measured by sieving, in which case the two largest dimensions areas least as large as mesh size, that is, the theoretical or actualsmallest sized mesh through which the particle could pass. The thirddimension can be measured by SEM or optical microscopic inspection ofthe whole (uncut) particles to insure that there is not a platelet orflake morphology whose average minimum dimension would fall below athreshold value.

DESCRIPTION OF PREFERRED EMBODIMENTS

Supports selected in the present invention are preferably selected to bestable in the reactor environment in which they are intended for use.Preferably, the supports are hydrothermally-stable, meaning that thesupport loses less than 15% of its surface area after 72 hours in waterat 150° C. More preferably, the support is hydrothermally-stable suchthat it loses less than 5% of its surface area after 72 hours in waterat 150° C. Preferred support materials include porous carbon and rutile.An especially preferred support is a porous, high surface area activatedcarbon, such as carbons with CTC values around 120%, available fromCalgon and Engelhard.

For good dispersion of the catalytic sites, the support preferably has ahigh surface area, preferably at least 100 m² per gram (cm²/g), and insome preferred embodiments between 100 and 2000 m²/g, as measured by BETnitrogen adsorption. Porous supports have high surface area.

A “porous” material has a pore volume of 10 to 98%, more preferably 30to 90% of the total porous material's volume. Preferably, at least 20%(more preferably at least 50%) of the material's pore volume is composedof pores in the size (diameter) range of greater than 20 angstroms, morepreferably 20 to 1000 angstroms. Pore volume and pore size distributionare measured by Mercury porisimetry (assuming cylindrical geometry ofthe pores) and nitrogen adsorption. As is known, mercury porisimetry andnitrogen adsorption are complementary techniques with mercuryporisimetry being more accurate for measuring large pore sizes (largerthan 30 nm) and nitrogen adsorption more accurate for small pores (lessthan 50 nm).

A metal oxide is disposed on the porous support. Preferably, for aqueousphase applications, the oxide contains at least one of Zr, Ti, Hf, Ta,Nb, Mo, and W. Preferably, the metal oxide contains at least 50%, morepreferably at least 90%, by mass of an oxide or oxides of one or more ofZr, Ti, Hf, Ta, Nb, Mo, and W. In some embodiments, the metal oxide issubstantially completely composed of an oxide or oxides of one or moreof Zr, Ti, Hf, Mo, and W. The rutile form of titania is especiallypreferred. In alternative embodiments, oxides of other elements such asSi, Al, Zn, Sn, V, Fe, U, Th, etc. may be used. The metal oxide ispreferably present in 1 to 25 weight %, more preferably 5 to 10 weightpercent of the total weight of the dried catalyst. Typically, the metalof the metal oxide is fully oxidized (for example TiO₂, ZrO₂, etc.) withterminal or bridging oxides; however, in less preferred embodiments theoxide could contain, in addition to oxygen, hydrogen in hydroxyls (whichmay be difficult to differentiate from hydrated oxides), sufides,cations, oxygen-containing anions, and the like.

The catalyst component includes a catalytically active metal, and thecatalyst component has a different composition than the metal oxide. Thecatalyst component may be any catalyst metal or catalyst compound. Formany embodiments, the catalyst component contains at least one elementselected from Pd, Ru, Rh, Pt, Re, Ni, Cu, Au, Ag, Co, Fe, Os, and Ir. Insome preferred embodiments, the catalyst component is a fully reducedmetal or mixture of fully reduced metals. The catalyst component ispreferably present in 0.1 to 10 weight %, more preferably 2.5 to 5.0weight percent of the total weight of the dried catalyst.

Various embodiments of the inventive catalyst provide unique structuralcharacteristics. Without intending to limit the scope of the invention,it is believed that, during catalyst preparation, kinetic and stericeffects limit distribution of the agglomerates, so that the metal oxideand the catalyst component are distributed mainly on the exterior of thesupport and through the larger pores and channels in the support. Underreaction conditions, the catalyst component remains associated with themetal oxide—thus stabilizing the catalyst. Some of the catalystcomponent may continue to migrate through the large pores and furtherinto the interior of the catalyst; although the explanation for this isunclear, it can be a beneficial effect since it serves to furtherdistribute catalyst component within the larger pores thus forming moresurface active sites for catalysis.

FIG. 1 shows scanning electron microscope (SEM) photomicrographs of across-section of freshly prepared catalyst. This catalyst was made by anincipient wetness catalyst preparation technique. This was done bytaking a 20.03 g sample of an Engelhard carbon (CTC=121%, 20-50 mesh,liquid holding capacity by the incipient wetness technique of 1.0 cc/g)to prepare a 2.5% palladium and 5% zirconia catalyst. The impregnationvolume of this preparation was about 20 ml. The amounts of palladium andzirconia are specified as final weight percent of the reduced metal onthe carbon support. Thus, the required weight of active metal precursorwas back calculated to determine the necessary weight of palladiumnitrate and zirconyl nitrate. For this example, 0.54 g of palladiummetal is required, and thus 3.71 of palladium nitrate stock solution wasrequired (at 14.57% palladium metal by weight). Also, 1.08 g ofzirconium metal was required, and thus 2.74 g of zirconyl nitrate arerequired. In a beaker, 8.32 g of water was added along with 0.84 g of70% nitric acid. 2.74 g of zirconyl nitrate was added and the beaker washeated and stirred on a hot plate without boiling until the solidsdissolve (˜80° C. for about 45 minutes). About 1.4 g of water wasevaporated during this process. This solution was then transferred to agraduated cylinder while still hot and 3.79 g of palladium nitrate wasadded to the cylinder. The solution was then heated and topped up to afinal volume of 20 ml. The solution remained under low heat for about 30minutes. The solution was then added in 1 to 2 ml aliquots to the jarcontaining the 20 g of carbon. After each addition, the jar was cappedand shaken until the carbon flowed freely in the vessel. Upon additionof the entire volume of solution, the carbon was sticky and slightlyclumped. The carbon sat closed at room temperature with intermittentagitation for 1.5 hours and appeared dry and mostly granular, with somematerial still adhering to the walls of the jar. The support was thenplaced uncapped in a vacuum oven set to 85° C. and 20 inHg vacuum andleft to dry overnight. The catalyst was reduced prior to use.

Samples for SEM analysis were prepared by cutting a resin embeddedcatalyst particle with an ultramicrotome. FIGS. 2 and 3 show the samecatalyst using an element mapping, x-ray spectroscopic technique. Thesefigures show the distribution of Si (in yellow, a contaminant), Zr(green), and Pd (red).

In this catalyst it can be seen that the Zr and the Pd are bothdistributed on the particle's exterior and in the larger pores withlittle or no distribution in the smaller pores, especially the smallpores furthest from the particle's surface. A limitation of thisanalytical technique is that the pore size is observed only in a singleplane. Passages to and from the observed pores will vary in size. Thus,while some relatively large pores appear devoid of Pd or Zr, this effectmay be caused by blockages in narrow passages that lead into these largepores, as they may be accessible only through micropores. The Pd and Zrconcentrate in the same areas of the catalyst. Surface area andstability of the Pd is increased by association with the zirconia.Another desirable effect that can be observed is the preferentialdistribution of metal oxide and catalyst metal on the particle exteriorand in the large pores; that is, preferred distribution in the mostaccessible areas of the catalyst resulting in desirable kinetics andproduct distribution. FIG. 3 shows that some internal pores may containsurprisingly high quantities of the catalyst metal. It may be that themacropores shown are cross-sectional elements of macropores thattraverse from the exterior of the carbon deep into the interior wherethe slice was taken. It is expected that these types of macropores areideal candidates for active catalytic surface, as they are areas of lowdiffusion limitations that would not be properly exploited in a typicalindustrial standard edge coat.

FIGS. 4 and 5a-5 c show the distribution of elements in a texturedcatalyst after about 4 hours of catalyzing the hydrogenation of succinicacid under hydrothermal conditions. Location 1, an internal pore, showsa high concentration of Zr with very little Pd. Location 2 is a densesection of the activated carbon, and, as expected, shows essentiallypure carbon. Analysis of location 3, the surface, indicates a relativelyhigh ratio of Pd to Zr.

In some preferred embodiments, the catalyst is characterized by one ormore of the following characteristics: a minimum, smallest dimension ofat least about 100 Pm, more preferably at least about 300 μm; at least70%, more preferably at least 80% of the catalyst component is withinabout 5 μm, more preferably about 2 μm, of 80% of the minimum area ofthe metal oxide. Preferably, at least about 5%, more preferably at leastabout 10%, of the catalyst component, and at least about 5%, morepreferably at least about 10%, of the metal oxide is disposed in poresthat are at least about 10 μm, more preferably at least about 20 μm,away from the exterior of the support. The foregoing properties areconducted by cutting a catalyst particle or monolith to obtain across-section of at least about 100 μm in both height and width. Themetal oxide is then imaged by an elemental analysis spectroscopictechnique, and the minimum area that encompasses 80% of the metal oxideis then identified. This area (or areas) is then increased by a 5 (or 2)μm margin around each area or areas. Then, the distribution of catalystin the cross-sectional area is imaged by an elemental analysisspectroscopic technique; at least 70% of the catalyst component iswithin the area of the 80% of metal oxide (including the margin).Amounts of each element is quantified by intensity. It is not necessarythat all cross-sections exhibit the characteristics described herein,but, for a desired catalyst, at least some cross-section has thesecharacteristics. Preferably, the 80% of the metal oxide plus 5 μm marginoccupies less than 90%, more preferably less than 40%, of the totalcross-sectional area. The converse preferably also occurs, that is, atleast 70%, more preferably at least 80%, of the metal oxide is withinthe minimum area of 80% of the catalyst component plus a 5 (or 2) μmmargin around each area or areas.

Preferably, at least about 50% of the catalyst component is within about10 μm of the exterior of the support. In some embodiments, some internalpores have at least 2 times, and in some cases at least 3 times, as muchof the catalyst component as compared with the metal oxide. In preferredembodiments, the majority, more preferably at least about 80%, ofcatalyst component, and/or the metal oxide, that is located within theinterior of the support (that is, that portion of the catalyst componentand/or metal oxide which is at least about 10 μm from the exterior ofthe support) is located in pores having at least one dimension of atleast about 5 μm. The foregoing values are measured based on SEManalysis of cross-sections of catalysts.

Some preferred embodiments of the inventive catalysts may,alternatively, be described with reference to the method by which thecatalyst is made. Alternatively, some preferred embodiments of theinvention can be described by reactivities. For example, in somepreferred embodiments, the catalyst exhibits a succinic acid conversionof at least 50% after 5 hours under the conditions set forth in Table 1.

Catalysts are preferably made by solution/colloid techniques. A poroussupport may be purchased or prepared by known methods. A metal oxide solis prepared or obtained. A sol may be prepared, for example, bydissolving a metal compound and adding water or changing pH to form asol. Each of the oligomeric or colloidal particles in the sol contain ametal and oxygen; these particles may also contain other components suchas halides, cations, etc. The sol could be prepared, for example, bydissolving a metal alkoxide, halide, etc. in an anhydrous solvent, thenadding sufficient water to form a sol. In some preferred embodiments,organic solvents are avoided and the sol is prepared only in water.Conditions for preparing sols will depend on the type of metal andavailable ligands. In some preferred embodiments, the sol is prepared atbetween about 10 and about 50° C. In some preferred embodiments, inaqueous solutions, the sol is preferably formed at a pH of between 1 and6, more preferably between 2 and 5. The metal oxide precursor sol iscontacted with the porous support. This could be done, for example, bydipping the support in the sol or colloid, or dispersing the sol in avolume of solvent equivalent to the insipient wetness of the support, sothat the solvent exactly fills the void fraction of the catalyst uponcontacting and is dried to deposit the metal oxide on the surface of thesupport. In the case of a particulate support, such as activated carbonpowders, the support and metal oxide precursor composition can be mixedin a suspension. The porous support is preferably not coated by avapor-deposited layer, more preferably the method of making the catalystdoes not have any vapor deposition step. The catalyst component can bedeposited subsequent to, or simultaneous with, the deposition of themetal oxide. The catalyst component can be impregnated into the supportin a single-step, or by multi-step impregnation processes. In apreferred method, the precursor for the catalyst component is preparedin a sol that is deposited after, or codeposited with, the metal oxideprecursor sol. In some preferred embodiments, the precursor for thecatalyst component is prepared under the same conditions as the metaloxide precursor sol, for example as an aqueous colloidal mixture in thedesired pH range. After the metal oxide and catalyst component have beendeposited, the catalyst is typically dried. Also, following deposition,if desired, the catalyst component can be activated or stabilized by anappropriate technique such as reduction under a hydrogen-containingatmosphere.

In its broader aspects, the invention includes heterogeneous, catalyzedreactions under any conditions. Preferably, to best take advantage ofthe unique characteristics of the inventive catalysts, at least onereactant is transported to the catalyst in a liquid phase, morepreferably in the aqueous phase (a subset of the liquid phase). Theliquid phase includes liquid, near critical, supercritical phases, and aneat phase comprised of a liquid primary reactant or a mixture of aliquid primary reactant and products. Additional reactants can becarried to the catalyst in the gas phase (such as hydrogen, etc.), innonaqueous solvents, or as solids. Preferred nonaqueous solvents includedioxane and ethers. Preferred reactants include maleic acid, succinicacid, lactic acid, malic acid, and their analogs and derivatives.“Aqueous phase” means that the feedstream containing the at least onereactant contains at least 20 mass %, more preferably at least 50%, andstill more preferably at least 80%, water. More preferably, thecatalyzed reaction occurs under hydrothermal conditions. In somepreferred embodiments the reaction occurs in the absence of organicsolvents. In some preferred embodiments, the catalyzed reaction occursin a temperature range of 120° C. to 260° C., more preferably 180 to220° C. In some embodiments, the aqueous phase has a pH of between 1 and6, more preferably 2 to 5. In some embodiments, the reaction occurs at atotal pressure of between about 1 atm and 210 atm. The reactions are notlimited to the type of reactor configuration, and may, for example, befixed bed, fluidized bed, batch, stirred tank reactor, membrane reactor,etc.

The catalyst of FIG. 1 was compared against a 2.5% palladium edge-coatedcatalyst from Engelhard. The two catalysts were tested in a 250 ml ParrReactor at 225° C. and 2500 psi (17 MPa) with 20% by weight succinicacid and hydrogen as the cover gas. Catalysts were reduced at 120° C.for 4 hours in an atmosphere of 20% hydrogen and 80% nitrogen. The tablebelow shows the individual properties of both tests:

TABLE 1 2.5% Pd/5% Zr on Engelhard 2.5% Pd on Carbon Catalyst TypeCTC121% Carbon (Engelhard edgecoat) Date May 28, 1998 Jun. 15, 1998Catalyst Loadout 2.51 g 2.53 g Feedstock Composition 81.67 g water/20.76g 81.95 g water/20.74 g succinic acid succinic acid OperatingTemperature 225° C. 225° C. Operating Pressure 2500 psi (17 MPa) 2500psi (17 MPa) Cover Gas Hydrogen Hydrogen Sampling Intervals1,2,3,5,8,12,24 hours 1,2,3,5,8,12 hours

The results for this particular example are shown below:

Sample (2.5 % Pd/5% Zr) (2.5% Pd edgecoat) Hour Conversion (%)Selectivity to GBL Conversion Selectivity to GBL 1 17.8 1  8.6 1 2 34.51 18.3 1 3 44.7 1 31.4 1 5 56.8 1 37.8 1 8 68.9 1 50.6 1 12  83.2 0.99363.3 1 24  98.2 0.919 no sample no sample

Another comparative test was run comparing 5% Rh/C and 5% Rh/5% Zr/C.Both catalysts were prepared by the incipient wetness method similar tothat described above and reduced in a 20% H₂ for 4 hours at 120° C. Bothcatalysts were tested using the same feedstock (20% aqueous diammoniumsuccinate) run under identical conditions (265° C., 1900 psig (13 MPa)under H₂ pressure, hourly sampling). The maximum yield of2-pyrrolidinone was 73% in each case, but the maximum yield occurredmore quickly for the textured catalyst. The calculated WWH (gconverted/g catalyst/hour) at 90% conversion was 2.05 for the 5% Rh/Ccatalyst and 3.61 for the 5% Rh/5% Zr/C catalyst.

As shown in the above-described examples, and other testing, it wassurprisingly found that the textured catalyst demonstrated unexpectedlysuperior results when compared to a conventional edge-coated catalysthaving the same weight % of catalyst component.

Closure

While preferred embodiments of the present invention have beendescribed, it will be apparent to those skilled in the art that manychanges and modifications may be made without departing from theinvention in its broader aspects. The appended claims are thereforeintended to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

What is claimed:
 1. A method of catalyzing a reaction comprising:passing an aqueous mixture comprising at least one reactant into areaction chamber; providing a catalyst within the reaction chamber, thecatalyst comprising a hydrothermally stable support having an exteriorsurface; a metal oxide; and a catalytic metal, at least 5% of thecatalytic metal being disposed within pores that are at least about 10μm away from the exterior surface of the support; reducing the at leastone reactant in the presence of the catalyst and under hydrothermalconditions, the reducing occurring at a pH of from about 1 to about 6;and obtaining at least one reduction product from the reaction chamber,wherein the reduction product obtained has a higher purity or a higheryield than where the reaction is conducted at a pH that is 4 or more pHunits from the pH of said aqueous solution.
 2. The method of claim 1wherein the aqueous solution has a pH between 2 and
 5. 3. The method ofclaim 1 wherein the reaction occurs in a temperature range of 120° C. to260° C.
 4. A method of catalyzing a reaction comprising: passing anaqueous solution comprising at least one reactant into a reactionchamber; providing a catalyst within the reaction chamber, the catalystcomprising: a porous, hydrothermally-stable support having a total porevolume, at least 20% of the total pore volume being contributed by poreshaving diameters of greater than about 20 angstroms; a metal oxidedeposited on the support; and a catalyst metal component; reacting theat least one reactant in the presence of the catalyst and underhydrothermal conditions; and obtaining at least one product from thereaction chamber.
 5. The method of claim 4 further comprising adding asecond reactant to the reaction chamber in a non-aqueous solvent.
 6. Themethod of claim 4 wherein the step of reacting occurs in a temperaturerange of 120° C. to 260° C.
 7. The method of claim 4 wherein the step ofreacting occurs at a pH of 1 to
 6. 8. The method of claim 4 wherein thereactant is completely dissolved in aqueous solution.
 9. The method ofclaim 4 further comprising addition of hydrogen gas to the reactionchamber.
 10. The method of claim 9 wherein the reactant comprisessuccinic acid.
 11. The method of claim 4 wherein the support comprisescarbon, and wherein the metal oxide comprises one or more of Zr, Ti, Hf,Ta, Nb, Mo, and W.